Percutaneous and laparoscopic surgical instrument

ABSTRACT

The present invention relates to a Radiofrequency surgical instrument comprising at least two dry electrodes ( 3  and  4,  or  3  and  5 ) and a electrode guiding device ( 6 ) comprising a main body ( 7 ), having a proximal end ( 73 ) and a distal end ( 74 ), and at least two insertion holes ( 8  and  81  or  82 ) guiding said electrodes ( 3  and  4,  or  3  and  5 ), said insertion holes ( 8  and  81  or  82 ) extending through the body ( 7 ).

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application is a continuation of U.S. application Ser. No.14/948,630, filed Nov. 23, 2015, which is a continuation of U.S.application Ser. No. 12/992,702, filed Nov. 15, 2010, which is theNational Stage of International Application No. PCT/EP2009/055984, filedMay 18, 2009, which further claims the benefit of European ApplicationNo. 08171007.1, filed Dec. 8, 2008 and U.S. Provisional Application No.61/053,788, filed May 16, 2008, the entire teachings and disclosure ofwhich are incorporated herein by reference thereto.

FIELD OF THE INVENTION

The present invention relates to a surgical instrument, in particular toa percutaneous and laparoscopic surgical instrument, and relates also toan electrode guiding device for such surgical instruments.

PRIOR ART AND RELATED TECHNICAL BACKGROUND

Radiofrequency (RF) therapy, is a well known non-invasive and outpatientprocedure that uses radio waves. Generally, it is used to treat cancer,more particularly for the ablation of tumors from different organs, e.g.breast, colon, lungs, pancreas, prostate, kidney.

In such procedure, electrodes are placed into contact with the tissue totreat and a current, from a RF generator, is applied to the tissue viathe electrodes. As the current passes, the tissue between the electrodesheats, a lesion is created, and the corresponding tissue is destroyed.

RF surgical devices are well known. Generally they are monopolardevices.

The device described in U.S. Pat. No. 5,507,743 may be a monopolar or abipolar device. In the bipolar form of the device, it comprises onestraight and one helical (coiled) electrode, the straight electrodebeing inside the helix formed by the helical one. In U.S. Pat. No.5,507,743, to increase the size of the lesion created, both electrodesare hollow with a plurality of fluid distribution ports to deliver, intoor onto the tissue to be ablated, a conductive fluid, such aschemotherapeutic agent or as an isotonic or hypertonic saline solution.

One of the main disadvantages of such RF surgical devices is that noconfinement of the lesion is achieved. Furthermore it is very difficultto predict how wide the lesion created will be.

In WO2004/100812, the bipolar RF device is a three elements devicewherein at least two of the elements are “dry” electrodes, i.e. nothollow and not able to deliver a conductive fluid. In the bipolar RFdevice described, the electrodes may be either both helical (coiled) andparallel one to another, or one helical and one straight. The bipolar RFdevice works by a cage effect allowing some confinement of the lesioncreated.

One of the main disadvantages of such bipolar RF surgical devicesworking with a cage effect, is the imprecise confinement of the lesioncreated as the positioning of the RF electrodes, to effectively ablatethe tissue, may be imprecise.

To ensure optimal performance, the axis of each electrode should beparallel; However, due to the piercing resistance of the skin, thetissue, or the organ to treat, and even if Radiofrequency electrodes aresharp and not deformable, the electrodes are prone to touch, or comeclose, one to another, leading to a misalignment of the electrodes and areduced performance of RF devices.

In addition, a controlled widening of the confinement is not possiblewith such bipolar RF surgical devices.

Aims of the Invention

The present invention aims to provide a percutaneous and laparoscopicsurgical device which does not have the drawbacks of the prior art.

Particularly, the invention aims to provide a RF surgical device withenhanced performance.

More particularly, the invention aims to provide a RF surgical devicewhich allow a defined confinement of the lesion created.

The present invention aims also to provide a RF surgical device withstabilised electrodes.

The present invention aims also to provide a device which ensure adimensional stability of the electrodes of a RF surgical device.

SUMMARY OF THE INVENTION

The present invention relates to a bipolar Radiofrequency surgicalinstrument comprising at least two dry electrodes, and a electrodeguiding device comprising a main body, having a proximal end and adistal end, and at least two insertion holes guiding said electrodes,said insertion holes extending through the body.

The term “dry electrode” should be understood as “solid electrode”,solid electrode meaning that the electrode is not hollow and not able todeliver a conductive fluid.

According to particular embodiments, the bipolar Radiofrequency surgicalinstrument may comprise one or a combination of any of the followingcharacteristics:

-   -   the at least two dry electrodes are helical;    -   at least one dry electrode is helical, and at least one dry        electrode is straight;    -   the at least two dry electrodes are arranged in a concentric        manner;    -   the shape and the size of the holes correspond to the shape and        the size of the corresponding dry electrodes;    -   the diameter of the holes do not exceed 10% of the diameter of        the electrodes;    -   the bipolar Radiofrequency surgical instrument comprises a RF        current generator, positioning means, controlling means,        location means and imaging means.

The present invention relates also to a device for guiding at least twoRadiofrequency electrodes of a bipolar Radiofrequency surgicalinstrument, said guiding device comprising a main body, having aproximal end and a distal end, and at least two insertion holes guidingsaid electrodes, said insertion holes extending through the body.

According to particular embodiments, the guiding device may comprise oneor a combination of any of the following characteristics:

-   -   the insertion holes are helical and arranged in a concentric        manner at the proximal end of said body;    -   the body comprises at least one helical insertion hole and one        straight insertion holes, said holes being arranged in a        concentric manner at the proximal end of said body;    -   the diameter of the insertion holes do not exceed 10% of the        diameter of the electrodes;    -   the body further comprises at least a supplementary hole at the        distal end of the body, said supplementary hole being straight;    -   the body is circular, and a first series of supplementary holes        are arranged, in a tangential manner, at the periphery of said        body;    -   the body further comprises a second series of supplementary        holes arranged in a tangential manner in respect to the first        series of supplementary holes;    -   the at least one helical insertion hole is formed by engaging a        threaded rod into a circular opening of the body;    -   the guiding device comprises a fixing part to fasten the guiding        device to the head of a laparoscopic surgical instrument or to        positioning means of a percutaneous surgical instrument.

The present invention relates also to a kit of parts comprising theguiding device according to the invention, and at least two dryRadiofrequency electrodes.

The present invention relates also to a method to remove a tumorcomprising the use of a Radiofrequency surgical instrument according tothe invention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the RF surgical device accordingto a first preferred embodiment.

FIG. 2 is a schematic representation of the RF surgical device accordingto a second preferred embodiment.

FIG. 3 is a schematic representation of the RF surgical device accordingto a third preferred embodiment.

FIG. 4 is a schematic representation of the cage effect whereby the RFsurgical device treats the tissue.

FIG. 5 is a schematic representation of the guiding device according toa first embodiment of the invention.

FIG. 6 is a schematic representation of the guiding device according toa second embodiment of the invention.

FIG. 7 is a schematic representation of the guiding device according toa third embodiment of the invention.

FIG. 8 is a schematic representation of a two pieces embodiment of theguiding device according to the invention.

FIG. 9 is a schematic representation of a “X, Y” head of a preferredembodiment of the RF surgical device.

DETAILED DESCRIPTION OF THE INVENTION

The bipolar Radiofrequency surgical instrument according to the presentinvention comprises at least one helical electrode (FIG. 1), preferablytwo helical electrodes 3 and 4 (FIG. 2), or an helical electrode 3 and astraight electrode 5 (FIG. 3) and a electrode guiding device 6.

Preferably, the bipolar RF surgical instrument is of the type describedin WO2004/100812 which is incorporated herein by reference. The RFsurgical device comprise a main body 1, stabilisation means 2 and atleast a set of electrodes which can be helical, more preferably twohelical electrodes, and even more preferably three helical electrodes.Optionally, it may further comprise a central member 5, which may or maynot be a straight electrode, and which is surrounded by the helicalelectrodes 3 or 4. When the central member 5 is an electrode, it can beused with either a single helical electrode, or with two or more helicalelectrodes.

The RF electrodes 3, 4 and/or the central member 5 are sharp, notdeformable, and rigid electrodes. They are “dry electrodes”, i.e. nothollow and not able to deliver a conductive fluid. Preferably, they aremade of metal, a biocompatible metal, preferably made of biocompatiblestainless steel. It may be for example surgical stainless steel type 304or type 316.

Preferably, the electrodes and/or the central member 5 are coated withan isolating polymeric compound, for example coated with TFE orpolyester. More preferably, they are coated along their length butexcept on their tip, for example over around one turn for helicalelectrodes and around 1.5 cm for the central member.

The helical electrodes 3 and 4 may have the same diameter or a diameterdifferent. Preferably, their diameter is between 1 and 2 mm, morepreferably around 1.2 mm, or around 2 mm. Preferably, their length is ofat least 15 turns, or a length of around 150 cm. The pitch is preferablya right-handed pitch, preferably of between 5 and 20 turns by cm. Thehelix formed by the helical electrodes 3 or 4 have preferably a diametercomprised between 8 to 24 mm. However, it is possible to adapt thediameter of the helix formed by the helical electrodes 3 or 4 accordingto the volume of the target tissue to treat.

The helical electrodes 3, 4 are wounded parallel one to the other andhave the same pitch. The helix formed by one of the electrode isarranged in a concentric manner in respect to the helix formed by theother, or others, electrodes.

Preferably, the central member 5 have diameter and length correspondingto those of the helical electrode 3 or 4. More preferably, the diameterof the central member 5 is around 1.5 mm.

The central member 5 can be placed at the centre of the helix formed bythe helical electrode 3 or 4.

In a preferred embodiment, the helical electrodes 3 and 4, and thecentral member 5 are fixed in the stabilisation means 2 by any suitablemeans.

In another preferred embodiment, the helical electrodes 3 and 4 arefixed in the stabilisation means 2 by any suitable means, while thecentral member 5 is removable.

Preferably, the helical electrodes 3 and 4 are glued in thestabilisation means 2 and are in contact with a connector which can bein electrical contact with a Radiofrequency generator.

As the central member 5 may be removable (FIG. 3), it may comprise atone end a connector which can be in electrical contact with aRadiofrequency generator.

The stabilisation means 2 of the RF surgical instrument have a hollowcylindrical shape, made of a biocompatible polymeric material, forexample poly-ether-ether-ketone (PEEK), polycarbonate or polyamide. Itfurther may comprise a channel through which the central member 5 canpass.

Preferably, the stabilisation means 2, comprising the helical electrodes3 or 4, is disposable. Preferably, the central member 5 is alsodisposable.

Each electrodes (electrodes 3, 4, and central member 5) can be activatedindependently one from the other to get a first pole (first electrode)and an second pole (second electrode), “activated” meaning that acurrent is applied into the electrode.

In on embodiment the first and the second pole are helical electrodes.In another embodiment, the first pole is a helical electrode 3 and thesecond pole is the central member 5.

When applying a current to at least one electrode of the RF surgicalinstrument according to the present invention, the surgical instrumentworks by a cage effect (FIG. 4). The heating created into the tissuegoes from the closest electrode to the centre to the furthermostelectrode. The tissue, which is in the cage formed by the electrodes, isthus destroyed, while the tissue outside the cage is safe.

The different combination between the type of electrodes (helical and/orstraight), and the different diameter of the helix formed by helicalelectrodes, present the advantage of having a RF surgical instrumentwhich can be easily adapted to the size of the tissue to treat.Furthermore, the use of the central member 5 presents the advantage ofhaving the possibility to treat a smaller tissue volume, for example incombination with a smaller helical electrode (electrode 4). It mayfurther present the advantage of modifying the shape of the treatedzone, from a square like shape, in case of use of helical electrodes, toa sharper shape.

The electrode guiding device 6 according to the invention presents theadvantage to maintain the dimensional stability of the electrodes bypreventing their deformation during the perforation of the skin or theorgan. Thus the confinement of the lesion created is precise and thetissue treated is as predicted. The precision of the treatment achievedis below 1 mm. It further enables an easier penetration of the helicalelectrodes 3 and 4 by making easier the penetration screw like movement.

The electrode guiding device 6 of the RF surgical instrument accordingto the invention comprises a main body 7 comprising at least two holes 8and 81 (FIG. 5) or 8 and 82 (FIG. 6), or three holes 8, 81 and 82 (FIG.7), extending through the body 7.

The body 7 comprises a front side 71, a back side 72, a proximal end 73and a distal end 74.

The body 7 has any suitable shape, preferably it is substantially round,but may also have, for example, a polygonal or a square shape. It ismade of any metal, or of polymeric material. Preferably, it is made oftitanium or stainless steel, or of a poly-ether-ether-ketone (PEEK),polycarbonate, or polyamide.

The body 7 comprises at least two holes 8 and 81, or 8 and 82, extendingthrough the body 7 from the front side 71 to the back side 72.Preferably, the holes are arranged at the primal end 73 of the body 7.

Through the body 7, and on the surfaces defined by the front side 71 andthe back side 72, the holes 8, 81, and/or 82 have a shape and a diameterenabling the electrodes 3, 4, 5 to go through. Preferably, their shapeand diameter correspond substantially to the shape and the diameter ofthe RF electrodes 3, 4, 5 to guide and which pass thought.

Through the body 7, the hole for a straight electrode is substantiallystraight, and the hole for a helical electrode is substantially helicalor substantially of a corkscrew shape, with either a left-handed or aright-handed pitch depending of the pitch of the helical electrodes. Onthe surfaces defined by the front side 71 and the back side 72, the hole82 may be round, square, oval, or octagonal.

The diameter of the holes 8 and 81 is substantially equal, orcorresponding, to the diameter of the helix formed by the correspondingelectrodes 3 and 4. The size of the opening forming the holes 8 and 81is substantially equal, or corresponding, to the diameter of thecorresponding electrodes 3 and 4, preferably the size of the opening donot exceed 10% of the diameter of the electrodes 3 or 4.

The diameter of the hole 82 is substantially equal, or corresponding, tothe diameter of the central member 5, and preferably do not exceed 10%of the diameter of the central member 5.

In a preferred embodiment, the body 7 of the guiding device comprisestwo helical holes 8 and 81 (FIG. 5).

In another preferred embodiment, the body 7 of the guiding devicecomprises one helical 8 and one straight hole 82 (FIG. 6).

In another preferred embodiment, the body 7 comprises two helical holes8, 81 and one straight hole 82 (FIG. 7).

However, the number of holes and their shape are not limited to thosedisclosed here as examples. The guiding device may comprise as manyholes, and as different, as RF electrodes are.

Preferably, the guiding device 6 according to the present inventioncooperates with the RF electrodes as described. However, the electrodeguiding device may be used with any RF surgical instrument having atleast two RF electrodes, straight and/or helical, being either hollow todeliver a conductive fluid, or dry, and having any size and any length.Nevertheless, the electrode guiding device is well suited to devicescomprising two helical electrodes wounded parallel one to the other.

The body 7 of the electrode guiding device has an overall size at leasthigher than the external diameter of the furthermost helical electrodefrom the centre of said body 7 (electrode 3 in FIGS. 1 to 3).Preferably, the body 7 has a size and a shape enabling his use with acatheter.

Preferably, the body 7 has a overall size of between 8 and 30 mm, athickness of between 1 and 3 cm. The spacing between two helical holesis around 20 mm.

In another preferred embodiment of the electrode guiding device 6according to the invention, the body 7 may comprise at least onesupplementary hole arranged at the distal end 74 of the body 7.Preferably, the body 7 comprises several straight holes laid in atangential manner at its periphery. More preferably, the body 7comprises two series of straight holes 10, 11, laid in a tangentialmanner at its periphery, the holes 10 of the first series being tangentto the periphery of the body 7, and the holes 11 of the second seriesbeing tangent to the holes 10 of the first series of holes (FIGS. 5 to7).

The supplementary hole 10 and/or 11 guide any other electrode, ananchoring member, or a needle, for example a straight needle, tointroduce a conductive fluid or chemotherapeutic agent into the tissuebefore, during, or after ablation, or a needle biopsy aspiration deviceor any sensor, for example temperature sensors, or any optical device,or illumination fibres.

In a preferred embodiment, the supplementary holes 10 and/or 11 guide astraight RF electrode. Preferably, the straight RF electrode is of thetype of the central member 5.

When the tissue to treat is bigger than the diameter of the biggesthelix formed by the outermost helical electrode 3, at least one straightRF electrode can be used, said straight RF electrode being guidedprecisely where wanted, thanks to the specific arrangement of thesupplementary holes 10 and/or 11 into the guiding device 6. To widen thevolume of tissue to treat, the RF current is applied either between thehelical electrode 3 and the supplementary straight electrode, or betweenthe central member 5 and the supplementary straight electrode.

Optionally, the guiding device further comprises a fixing part 9, toallow the guiding device 6 to be handheld, or to be fixed to apercutaneous surgical instrument or a laparoscopic surgical instrument.

The body 7 of the electrode guiding device may be made either of onepiece, or made of the assembly a two elements, one corresponding to thefront side 71 and the other corresponding to the back side 72 of thedevice, the two elements being assembled by any suitable method.

The one piece body 7, or the two elements body 7, may be produced by anysuitable method, for example by extrusion, by moulding or bystereolytography.

In a preferred embodiment, the hole 8, 81, 82 and the supplementary hole10 or 11 are formed during the process to manufacture the body 7. Inanother embodiment, the hole 8, 81, 82 and the supplementary hole 10 or11 are drilled, by any suitable means, into the mass of the one piecebody 7, or in the two elements corresponding to the front side 71 andthe back side 72 of the body 7, the holes being drilled before or afterthe assembly of the two elements of the body 7.

In another embodiment, the holes 8, 81 or 82 are not drilled but areformed by the assembly of a one piece body 12, or a front side and backside elements assembly, having a circular opening 13, and a threaded rod14 engaged in said circular opening 13 (FIG. 8). Preferably, thethreaded rod 14 is engaged by force in the opening 13 and fixed to thebody 7, for example by heat welding or by mean of a biocompatible glue.

Preferably, the threaded rod 14 is made of the same material as the oneof the body 7, or as the one of the front side and back side elements,for example, made of PEEK.

The diameter of the opening 13 and the external diameter of the threadedrod 14 are chosen to fit the external diameter of the helical electrodeto guide. Furthermore, the length of the threaded rod 14 substantiallycorresponds to the thickness of the body 7, and its pitch substantiallycorresponds to the pitch of the helical electrode, in terms of dimensionand type of pitch (either left-handed or right-handed thread).

Preferably, the threaded rod 14 further comprises a hole 82, which maybe an helical hole or a straight hole. The threaded rod 14 may comprisea helical and a straight hole. The hole 82 may be drill in the threadedrod 14, or may be formed by the engagement a threaded rod in an openingat the centre of the threaded rod 14.

The guiding device 6 may be fastened by any suitable means to alaparoscopic instrument, for example an endoscope, to a positioning headof a percutaneous surgical instrument, or to be held by hand.Preferably, this fastening is achieved by a fixing part 9 of the guidingdevice 6.

Preferably, the electrode guiding device is disposable.

The RF surgical instrument, and the electrode guiding device, accordingto the invention, may be parts of a more complex surgical instrument.

In a preferred embodiment, the RF surgical instrument, and the electrodeguiding device, according to the invention, may be parts of alaparoscopic surgical instrument, for example an endoscope device.Therefore, the electrode guiding device 6 may be fixed to the head ofthe endoscope by, for example, a fixing part 9, which may have anysuitable shape and size. The front side 71 of the guiding device 6 isplace against the organ to treat and the electrodes extend out throughthe head of the endoscope device, engage, and extend out through, theelectrode guiding device 6, and penetrate into the organ in a screw-likemovement for helical electrodes, or a straight movement for a straightelectrode, as deep as necessary to reach the zone to treat.

The laparoscopic surgical instrument may further comprise a RF currentgenerator, and optionally, spatial location means, optical means, biopsyaspiration means, sensors and/or computer means.

In a preferred embodiment, the RF surgical instrument, and the electrodeguiding device, according to the invention, may be parts of apercutaneous surgical instrument. Therefore, the surgical instrumentfurther comprises a RF current generator, and optionally, positioningmeans, controlling means, location means, imaging means, and computermeans.

In percutaneous applications, the front side 71 of the guiding device 6is place against the skin and is hand-held, for example by the fixingpart 9, said fixing part 9 having any suitable shape and size. Then, theelectrodes 3, 4 and/or 5 are engaged into the holes of the guidingdevice, and extend out through the guiding device 6 to penetrate throughthe skin in a screw-like movement for helical electrodes, or a straightmovement for the straight electrode, as deep as necessary to reach thezone to treat. However, this operation may be more automated by usingpositioning means and controlling means. The RF surgical device mayfurther comprise location means and imaging means.

Preferably, the positioning means comprise a “X, Y” head 12 (FIG. 9), ora robot arm, to which the electrode guiding device 6 is fixed, forexample by using the fixing part 9 of any suitable shape and sizeallowing its fastening to the “X, Y” head 12 or robot arm.

The location means, comprising for example a ultrasound probe coupled toimaging means, allow to get the exact position of the tissue to treatand give a reference point to insure the precise positioning of theelectrodes using the “X, Y” head 12, before and after the penetration ofthe electrodes 3, 4, 5. Preferably, the location means are controlled bythe computer means.

The front side 71 of the guiding device 6, fastened to the “X, Y” head12, for example by the fixing part 9, is place against the skinprecisely at the point of entry determined by location means, at thelevel of the tissue to treat, or the area chosen for the treatment.Then, the electrodes 3, 4 and/or 5 extend out through the electrodeguiding device 6, and penetrate through the skin as deep as necessary toreach the zone to treat.

The “X, Y” head 12, and/or the movement of the electrodes 3, 4, 5, maybe hand-operated, for example by the operator of the surgicalinstrument, or automatically operated using the controlling means, whichmay comprise for example a stepper motor which may be controlled by thecomputer means.

Preferably, in either the laparoscopic or percutaneous embodiments, thetreatment of the tissue or the organ may be followed by the locationmeans coupled to the imaging means.

If necessary, to widen the volume of the area to treat, without beingobliged to remove the electrodes and to readjust the position with the“X, Y” head 12, one or more straight electrodes may be used. Thesesupplementary electrodes are precisely positioned thanks to thesupplementary hole 10 and/or 11 of the guiding device 6. Thus, the areatreated is widened while the skin perforation is reduced to a minimum.

The electrode guiding device 6 according to the invention presents theadvantage of allowing thus a precise electrodes positioning in respectto the tissue to treat, as it is an alternate solution to thetraditional grid used to guide straight electrodes of percutaneoussurgical instrument.

It has also the advantage of giving the possibility to widen the treatedarea by guiding at precise locations supplementary electrodes.

The RF surgical instrument, according to the invention comprising theguiding device 6, presents the advantage of having enhancedperformances. It also has the advantage of being adaptable to any sizeor shape of tumours to treat. It also has the advantage of beingminimally invasive.

The RF surgical instrument, according to the invention, may preferablybeen used to treat prostate, kidney or breast cancer.

1. A surgical assembly, comprising: a first electrode, wherein the firstelectrode is rigid and is shaped as a helix, the helix having a firstpitch, a second electrode arranged concentric with the first electrode,and an electrode guiding device, comprising: a body comprising a firstthrough hole, wherein the first through hole is cylindrical with adiameter corresponding to an external diameter of the helix, and aninsert fittingly received in the first through hole, wherein the insertcomprises a guide provided on a periphery of the insert, wherein theguide is representative of a helical pathway having a second pitchcorresponding to the first pitch, and wherein the insert comprises asecond through hole concentric with the first through hole.
 2. Thesurgical assembly of claim 1, wherein the first electrode is receivablein the first through hole, wherein the first through hole allows foradvancing the first electrode therethrough by screw-like movement. 3.The surgical assembly of claim 2, wherein the second electrode isreceivable in the second through hole.
 4. The surgical assembly of claim1, wherein the second electrode is straight.
 5. The surgical assembly ofclaim 4, wherein the second through hole is cylindrical.
 6. The surgicalassembly of claim 1, wherein the second electrode shaped as a helixhaving an external diameter smaller than the external diameter of thehelix of the first electrode.
 7. The surgical assembly of claim 6,wherein the second through hole has a shape substantially correspondingto a shape of the second electrode, wherein the second electrode isreceivable in the second through hole.
 8. The surgical assembly of claim1, comprising a fixing system allowing for securing the electrodeguiding device to a support.
 9. The surgical assembly of claim 8,wherein the fixing system is integral with the body.
 10. The surgicalassembly of claim 8, wherein the support is an XY stand.
 11. Thesurgical assembly of claim 1, wherein the body comprises a third throughhole arranged at a periphery of the first through hole.
 12. The surgicalassembly of claim 1, wherein the external diameter is between 8 mm and24 mm.
 13. The surgical assembly of claim 1, wherein the pitch isbetween 5 turns per cm and 20 turns per cm.